igneous
Weathered volcanic rock, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; probable basalt (plagioclase ± pyroxene, with alteration minerals)
AI-generated identification · may be incorrectGray-brown, dull, fine-grained and vesicle-poor in the visible surface; likely hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The crumbly pale surface suggests strong weathering or alteration, so identification from the image is provisional.
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Physical properties
Gray-brown, dull, fine-grained and vesicle-poor in the visible surface; likely hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The crumbly pale surface suggests strong weathering or alteration, so identification from the image is provisional.
Formation & geological history
Formed when lava cooled rapidly at or near Earth’s surface, producing microscopic crystals; commonly Cenozoic to older, depending on locality. Weathering has oxidized and softened the exposed surface.
Uses & applications
Used as aggregate, road material, riprap, and building stone when fresh; this small weathered fragment has mainly educational or casual collecting value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and volcanic plateaus.
Field identification & locations
Look for a dense dark interior, fine texture, and possible tiny feldspar or pyroxene grains; a streak, fresh fracture, magnetism, and acid test can help distinguish basalt from andesite or altered volcanic ash. Common worldwide in volcanic regions.
